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Loopback testing
- 1. Loopback Testing Testing Loopbacks Using OptoTest Equipment
- 2. www.optotest.com Background A loopback is an optical component that routes fiber optic lines from port(s) of a connector to other ports of that connector. § These can have additional attenuation induced Used for BER testing § Routes transmit ports back to receive ports § With additional attenuation it can simulate a worst-case link loss for stress testing transceivers Used for OTDR testing of links § Terminates a long transmit link to a long receive link and allows the technician to diagnose both links without needing to connect OTDR to opposite side of receive link
- 3. www.optotest.com Structure Duplex LC MTP® Loopback (4ch) One link loops from one port to the other Multiple ports routed to other ports of the same connector. In this example fibers 1 to 4 are routed back to fibers 9 to 12
- 4. www.optotest.com Transceiver testing MTP Duplex LC To test a transceiver, connect a loopback directly to the transceiver. With this, one can test bit error rate.
- 5. www.optotest.com § IL system (light source and power meter) § RL if necessary. § Channel count at least equivalent to number of links of the loopback § Duplex LC has one link (simplex system fine) § MTP loopback (8 ports populated) has 4 links § For highest accuracy MTP requires large area detector § Typically link loss is tested § Measured for the entire link and both connections of the loop back § For MTP a fanout is needed as well as a return MTP ideally § Use a fanout with the channels populated according to loopback § Launch cord with MTP connectors fanned into MTP connector § Return Loss § RL measurement is typically a combination of input and output connectors due to short internal fibers Testing Loopbacks Equipment needed
- 6. www.optotest.com Testing Loopbacks (LC) Reference Setup Measurement Setup LoopbackThis measures total IL of the Link: fiber loss and connector loss for both connections on the loopback. § To reference, use a single reference cord connected to the OPM and reference IL and RL § To measure, connect the reference connector to the input connector of the loopback and connect a receive cord from the output port of the loopback to the OPM.
- 7. www.optotest.com Cable setup • Equipment cord • Connects from the source to the launch cord Testing Loopbacks (MTP) 4 Fiber fanout (Only Ch1 to Ch4)
- 8. www.optotest.com Cable Setup (Cont.) • Launch/Return cord Testing Loopbacks (MTP)
- 9. www.optotest.com Equipment setup Testing Loopbacks (MTP) Type A Adapter Key-up/Key-down
- 10. www.optotest.com Referencing Testing Loopbacks (MTP) Type A Adapter Key-up/Key-down
- 11. www.optotest.com Measurement Testing Loopbacks (MTP) Type A Adapter Key-up/Key-down Type A Adapter Key-up/Key-down
- 12. www.optotest.com Measurement Results Insertion loss § This will be a combination of both connectors and whatever loss inside the loopback. Return Loss § Depending on length of fiber inside the loop back, this could be a combination of both interfaces.